DNA Structure and Nucleotides Quiz

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Questions and Answers

What is the length of the double-stranded DNA that wraps around a nucleosome core particle?

147 nucleotide pairs (correct)

80 nucleotide pairs

200 nucleotide pairs

170 nucleotide pairs

Which histone proteins are included in the nucleosome core particle?

H1, H2A, H2B, H3, H4

H1, H3, H4, H5

H2A, H2B, H3, H4 (correct)

H2A, H3, H4, H5

What model describes how nucleosomes are packed into a chromatin fiber?

Zigzag model (correct)

Spiral model

Linear model

Beads on a string model

What forms the linkages between nucleosomes in the chromatin structure?

Histone tails Signup and view all the answers

What is the approximate separation distance between nucleosomes?

80 nucleotide pairs Signup and view all the answers

What type of bonds connect the nucleotides in a DNA strand?

Phosphodiester bonds Signup and view all the answers

Which nitrogen-containing bases are found in DNA?

Adenine, Thymine, Cytosine, Guanine Signup and view all the answers

What charge does a phosphate group in a nucleotide carry?

Negative charge Signup and view all the answers

What is the correct sequence of nucleotides for a DNA chain starting with the base Adenine at the 5' end?

AGCTT Signup and view all the answers

Which part of the nucleotide is known to be covalently linked through phosphodiester bonds?

Sugar to phosphate Signup and view all the answers

What is the main structural feature of the DNA molecule?

Two long polynucleotide chains running antiparallel Signup and view all the answers

How are base pairs held together in the DNA double helix?

Hydrogen bonds Signup and view all the answers

Which component is not present in a nucleotide?

Amino acid Signup and view all the answers

What is the approximate length of human genome DNA in nucleotide pairs?

3.1 x 10^9 Signup and view all the answers

Which of the following describes heterochromatin?

Condensed and transcriptionally inactive Signup and view all the answers

How many genes coding for proteins are estimated to be in the human genome?

20,000 Signup and view all the answers

What characterizes the interphase of the cell cycle?

Cell growth and DNA replication Signup and view all the answers

Which protein is NOT part of nucleosomes?

Chaperone proteins Signup and view all the answers

What is the extent of DNA compaction during mitosis?

7000x Signup and view all the answers

What are nucleosomes fundamentally associated with?

Chromosome structure Signup and view all the answers

How long would chromosome 22 extend if laid out as one long double helix?

1.5 cm Signup and view all the answers

What form does chromatin take during interphase?

Diffuse mass Signup and view all the answers

Which phase of interphase is characterized by DNA copying?

S phase Signup and view all the answers

What type of bond is formed when two nucleotides are linked together?

Phosphodiester bond Signup and view all the answers

What happens to the pyrophosphate group during the reaction?

It is hydrolyzed, releasing energy. Signup and view all the answers

In the double helix structure, what holds the two strands together?

Hydrogen bonds between base pairs Signup and view all the answers

Which of the following statements about base pairing is correct?

Guanine pairs with Cytosine through three hydrogen bonds. Signup and view all the answers

What characteristic of the two polynucleotide chains allows for proper base pairing?

They are anti-parallel. Signup and view all the answers

What is the arrangement of the sugar-phosphate backbones in the double helix?

On the outside of the structure Signup and view all the answers

How many hydrogen bonds form between Adenine and Thymine?

Two Signup and view all the answers

Why is pairing a two-ring base (purine) with a single-ring base (pyrimidine) energetically favorable?

It maintains a constant width between the backbones. Signup and view all the answers

What is the primary function of telomeres in eukaryotic chromosomes?

To protect the ends of chromosomes from unraveling Signup and view all the answers

How many pairs of homologous chromosomes do typical eukaryotic cells possess?

22 pairs Signup and view all the answers

What is the structure formed by DNA tightly bound with proteins called?

Chromatin Signup and view all the answers

What is the role of the centromere in chromosomes?

It separates the chromatids during division Signup and view all the answers

What is the significance of the number of base pairs in a complete turn of a DNA helix?

It contributes to the stability of the helix structure Signup and view all the answers

What unique feature characterizes the two grooves of the DNA molecule?

One is larger than the other Signup and view all the answers

Which of the following statements is true concerning the karyotype of chromosomes?

Karyotypes line up chromosomes in numerical order Signup and view all the answers

What happens to telomeres during multiple cell divisions?

They lose a bit of their DNA Signup and view all the answers

Study Notes

DNA Structure

DNA (Deoxyribonucleic acid) consists of two long polynucleotide chains made of four nucleotide types.
Each chain is defined as a "DNA strand" and the strands run antiparallel, connected by hydrogen bonds at their bases.
Nucleotides comprise a five-carbon sugar, a phosphate group, and a nitrogenous base; they form a sugar-phosphate backbone via covalent bonds.

Nucleotides

Nucleotides include adenine (A), cytosine (C), guanine (G), and thymine (T), with ribose sugar in RNA.
Nucleotides are negatively charged due to the phosphate group; they connect through phosphodiester bonds between the 5' and 3' carbon atoms of the sugar rings.

Double Helix Structure

DNA twists into a right-handed double helix, with two grooves: major and minor.
A complete turn of the helix includes approximately 10.4 base pairs.
Bases pair based on size and bonding: A pairs with T (two hydrogen bonds), while G pairs with C (three hydrogen bonds), allowing stable helical formation.

Chromosome Organization

Eukaryotic cells have 22 pairs of homologous chromosomes plus one pair of sex chromosomes.
Each chromosome comprises a single, long DNA molecule complexed with proteins to form chromatin, essential for gene expression and DNA maintenance.

Karyotype

Chromosomes can be visualized and arranged in numerical order to create a karyotype, aiding in analysis of genetic information and irregularities.

Centromeres and Telomeres

Centromeres serve as attachment points for sister chromatids during cell division, ensuring proper chromosomal alignment.
Telomeres protect chromosome ends from degradation, shortening slightly with each cell division to maintain genome integrity.

Chromatin States

Chromatin exists in two forms: heterochromatin (condensed and transcriptionally inactive) and euchromatin (decondensed and active in transcription).
During interphase, chromatin remains tightly packed but can decondense to facilitate access to specific DNA sequences.

Nucleosomes

Nucleosomes are the fundamental units of chromatin, consisting of DNA wrapped around histone proteins.
Each nucleosome contains an octamer of histones (H2A, H2B, H3, and H4) around which 147 nucleotide pairs of DNA coil.

Packing and Compaction

Nucleosomes are separated by linker DNA, with a repeating structure occurring every 200 nucleotide pairs.
Chromatin often adopts a hierarchical structure, forming looped domains that promote further compaction through interactions between histone tails.

Summary of DNA Packaging

DNA molecules are compacted efficiently within the nucleus using proteins, achieving approximately 7000-fold reduction from their extended state.
Understanding nuclear structure, including the nuclear envelope and lamina, aids in comprehending cellular organization and gene regulation.

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Description

Test your knowledge on the structure of DNA and the role of nucleotides. This quiz covers the double helix formation, nucleotide composition, and base pairing rules. Perfect for students studying molecular biology or biochemistry.